Glass microbubbles, variously also known in the art as “hollow glass microspheres” or “glass microballoons”, typically have low specific gravity, satisfactory heat resistance, heat insulating properties, pressure-resistance (e.g., crush strength) and impact resistance, and may achieve superior physical properties when substituted for conventional fillers. They are used in applications such as molding parts (e.g., including a molding compound for electric household appliances, portable electronic devices and automobiles), putties, sealing materials, a buoyancy material for ships, a synthetic wood, a reinforcing cement outer wall material, a light weight outer wall material, and artificial marble. Also, due to the structure of hollow particles, glass microbubbles may have a low dielectric constant that can be imparted as a bulk property to compositions in which they are contained.
Glass microbubbles can be prepared using a variety of processes and materials. In some cases, the product made from these processes and materials is multi-cellular, weak, not chemically durable, and/or has other limiting characteristics. For some applications, consistently higher quality single-cell glass microbubbles are required. It is particularly desirable to obtain high strength to density ratios.
Glass microbubbles are typically formed by heating glass frit and/or agglomerated oxides and inorganic salts, optionally containing a blowing agent (i.e., also known as a “feed”) in a flame, thereby forming glass microbubbles. The microbubbles thus formed, known in the art as “raw product”, are typically accompanied by, among other things, unexpanded glass beads and broken glass microbubbles. The raw product may be further processed, for example, by classification and/or flotation to further purify and isolate the glass microbubbles.
Attempts to reduce costs in the glass microbubbles industry while simultaneously achieving acceptable or improved physical properties (e.g., crush strength and/or density) have been for many decades, yet there remains a need for glass compositions and methods with reduced cost and acceptable physical properties.